Observational Test of Coronal Magnetic Field Models. I. Comparison with Potential Field Model

Abstract

Recent advances have made it possible to obtain two-dimensional line-of-sight magnetic field maps of the solar corona from spectropolarimetric observations of the Fe xiii 1075 nm forbidden coronal emission line. Together with the linear polarization measurements that map the azimuthal direction of the coronal magnetic field projected in the plane of the sky containing Sun center, these coronal vector magnetograms allow for direct and quantitative observational testing of theoretical coronal magnetic field models. This paper presents a study testing the validity of potential-field coronal magnetic field models. We constructed a theoretical coronal magnetic field model of active region AR 10582 observed by the SOLARC coronagraph in 2004 by using a global potential field extrapolation of the synoptic map of Carrington Rotation 2014. Synthesized linear and circular polarization maps from thin layers of the coronal magnetic field model above the active region along the line of sight are compared with the observed maps. We found that the observed linear and circular polarization signals are consistent with the synthesized ones from layers located just above the sunspot of AR 10582 near the plane of the sky containing the Sun center.

Coronal magnetic fields from the inversion of linear polarization measurements

“…2 of Lin et al (2004) with PAH (i.e., the Position Angle in the Heliocentric coordinate system) of 296, 291, 286, 281, and 276 degrees, separately. The coordinate system and the parameters used in the paper Liu & Lin (2008). Similar to results of the region PAH 286 (Liu & Lin 2008), the profiles of LP vs. z values (in unit of layer, i.e., lyr; Layerbest) in the other four regions also show a clear dip (Liu 2009).…”

“…The coordinate system and the parameters used in the paper Liu & Lin (2008). Similar to results of the region PAH 286 (Liu & Lin 2008), the profiles of LP vs. z values (in unit of layer, i.e., lyr; Layerbest) in the other four regions also show a clear dip (Liu 2009). The identical peak/valley locations were noticed for different profiles.…”

“…It can be seen that most derived IR emission sources were mainly distributed at around z = 120 where the sunspot region was located near the solar limb on the photosphere (Liu & Lin 2008). If we presume that the basic coronal structures in EUV wavelengths be kept stable and the same during the days before the solar limb SOLARC observation, it would be interesting to compare the inferred IR emission sources with the EUV bright features (Liu 2009).…”

“…A line-of-sight (LOS) coronal magnetogram was shown by Lin et al (2004) as one of the first results taken by SOLARC. Liu & Lin (2008) studied in detail a limb coronal region by comparing the observed circular and linear polarizations with the synthesized maps based on potential field model. The best consistence for both linear and circular polarizations was found at the layer in the corona above a sunspot near the solar limb, indicating that local coronal magnetic fields may be revealed from the IR polarization data with the proper coronal magnetic field inversion method.…”

“…Our recent studies focused on this issue are briefly reviewed in this paper. Liu & Lin (2008) first evaluated the validity of potential field source surface model applied to one of five limb regions in the corona by comparing the theoretical polarization maps with SOLARC observations in the IR Fe XIII 10747Å forbidden coronal emission line (CEL). The five limb coronal regions were then studied together in order to study the spatial relation between the bright EUV features on the solar disk and the inferred IR emission sources, which were obtained from the inversion of the SOLARC linear polarization (LP) measurements (Liu 2009).…”